Transmission configurations in the form of torque split transmissions in the form of overlay transmissions are known in the number of versions.
We refer to the following representative publications:                1. EP 1 333 194        2. DE 197 55 612 A1        3. EP 1 061 287 A2        4. DE 43 08 761 A1        5. De 887 457 C        6. DE 10 2004 022 204 B3        
The design according to DE 197 55 612 A1 comprises a transmission input shaft, a continuously variable speed transforming transmission connected to the transmission output shaft in the form of a traction device which comprises an input and an output, whereby the input is rotationally fixed to the transmission input shaft, a fixed gear step and an overlay transmission with a first input stage which is rotationally connected to the output of the continuously variable speed transforming transmission. Further, a second input stage is provided which optionally is connectable with the transmission input shaft to the fixed gear step using a first coupling, and an output stage which is rotationally fixed to the transmission output shaft. In this example, the fixed gear step on the transmission side is rotationally fixed with the transmission input shaft and with respect to the output side fixed gear step arranged on the first coupling in such a way that it optionally connects the second input stage of the overlay transmission on the output side with the fixed speed transforming gear. Using this solution it is possible to provide a reliable range-change transmission in a simple fashion. The solution offers the advantage of avoiding in a range-change transmission combining a continuously variable speed transforming transmission and an overlay transmission with a so-called geared-neutral range the creating of high contact speeds in the area of the first coupling because it is arranged at a position after a corresponding gearing of the high RPM of the driveshaft to the low RPM by the fixed gear step. The above reduces wear and increases the service life of the first coupling. However, there is a significant disadvantage in the direct coupling between the continuously variable transmission, also known as CVT, and the transmission input and therefore the drive shaft. The continuously variable transmission is therefore always connected to the RPM of the motor. Removing load from the overlay transmission in a range of higher RPM of the drive shaft and/or lower transmission ratios of the continuously variable transmission is achieved by providing a second coupling, which optionally connects the first input stage with the output stage of the overlay transmission. This creates a rigid connection between the output shaft of the continuously variable speed-transforming transmission and the drive shaft, by which the overlay transmission is bridged in the torque flow. Another basic problem of power transmission through the continuously variable speed-transforming transmission consists of the fact that due to its size only a maximum allowable torque can be transmitted, otherwise at very high loads impermissible slippage is observed which can lead to increased wear on the transmission. Due to the direct coupling of the continuously variable transmission to the transmission input, this transmission is always subject to the conditions provided on it. That means that the input of the CVT has the same RPM applied to it at the transmission input and therefore from the motor. Publication EP 1 333 194 reveals a transmission unit whose design is modified in such a way that the load on the traction device is significantly reduced thus insuring the transferability of high torques, in particular torques higher than could be guaranteed in the design according to DE 197 55 612 A1. In this version the transmission unit is also designed as an overlay transmission unit. This version comprises a transmission input and a transmission output, further two overlay transmissions arranged between the transmission input and the transmission output and connected. Each of the two overlay transmissions is designed as a three-shaft planetary gear. Both are connected to a four-shaft planetary gear. Further, a continuously variable transmission is connected between the first overlay transmission and the second overlay transmission in the form of a traction device. Each planetary gear comprises a sun gear, a ring gear, planetary gears and a flange. The individual shafts are formed by the sun gear, ring gear or flange of the respective overlay transmission. The transmission input is rotationally fixed with a second shaft of the first overlay transmission and a first shaft of the second overlay transmission. The transmission output is rotationally fixed with a second shaft of the first overlay transmission and a second shaft of the second overlay transmission. The coupling of the two three-shaft planetary gears to a four-shaft planetary gear is done by coupling the first and second shafts of the first and second overlay transmissions. The term shaft must be understood in functional terms, whereby it is understood to mean either the individual elements of the planetary gears—sun gear, ring gear or flange, or with elements rotationally fixed to them, for example, in the form of shafts or hollow shafts. Depending on working condition, the individual shafts assume the function of inputs or outputs. For example, for power transmission from the transmission input shaft to the transmission output shaft via the continuously variable transmission, the first overlay transmission comprises one input and two outputs. The input is formed by the first shaft, while the output which is connected at least indirectly to the continuously variable transmission is formed by the third shaft, and the second shaft is formed by the output which is rotationally fixed to the transmission output shaft. In this working condition, the second overlay transmission comprises one input and one output, whereby the input is also connected to the transmission input shaft and is formed by the first shaft of the second overlay transmission and the output of the second shaft. The third shaft is connected to the continuously variable transmission. Further, means are provided to change the transmission ratio. One of the two overlay transmissions—the first or second overlay transmissions are provided with planetary gears intermeshing in pairs between the sun gear and the ring gear. The planetary gears intermeshing in pairs are also known as double planetary gears. Due to the version of a second overlay transmission with planetary gears intermeshing in pairs designed as a planetary gear which are also known as double planetary gears, it is guaranteed for the section of the total operating range that the CVT operates with maximum RPM, whereby it is also possible to change the gear ratio of the individual discs can be done at maximum motor RPM, that means, that it is possible to turn one over zero and therefore it is also possible with the inventive transmission to change direction of rotation as well as geared-neutral. The double design offers the advantage that in an increase in RPM on the output connected to the continuously variable transmission, in particular the ring gear, this planetary gear brings about a decrease corresponding to the design of the other planetary gear on the output connected to the other planetary gear on the other planetary gear, in particular the ring gear. According to this version, it is however not possible to have the CVT work with maximum RPN a number of times over the entire operating range.
Another embodiment of the range-change transmission is known from DE 10 2004 022 204 B3. This patent comprises a simple planetary gear, three spur gears, two coupling devices and a contact transmission. The output shaft is optionally connected via both coupling devices with the sun gear or ring gear shafts.
The task of the invention is to create a range-change transmission from a continuously variable transmission, in particular in the form of a traction device and planetary gear sets which is characterized by a high overall distribution and further by a relatively simple construction and one which saves space in the axial direction. Further, a very high load relief must be calculated in the second operating range with a large amount of time which corresponds to the operating range which is outside the starting area and further to realize operating above zero so that additional means are not required to realize reverse motion.